Approximately 1,200 women who meet the inclusion criteria will be enrolled in this double-blind, randomized, multicenter, two-year study to compare the safety and efficacy of daily oral alendronate vs. 35 mg. alendronate twice weekly vs. 70 mg alendronate once weekly in increasing lumbar spine density in ambulatory postmenopausal women with osteoporosis and low bone density. About 25 women will be recruited to participate at the University of Chicago site.